Typically, linear ion traps store ions using a combination of a radial RF field applied to the rods of an elongated rod set, and axial direct current (DC) fields applied to the entrance end and the exit end of the rod set. Linear ion traps enjoy a number of advantages over three-dimensional ion traps, such as providing very large trapping volumes, as well as the ability to easily transfer stored ion populations to other downstream ion processing units. However, there have been problems with the use of such linear ion traps.
One such problem is that it has not typically been possible to simultaneously store positive ions and negative ions in a linear ion trap. This problem is due to the fact that while a particular axial DC field may provide an effective barrier to an ion of one polarity, the same DC field will accelerate an ion of opposite polarity out of the linear ion trap. Thus, linear ion traps relying on DC barrier fields have not typically been used to simultaneously store ions of opposite polarities.
Accordingly, there remains a need for linear ion trap systems and methods of operating linear ion traps that allow ions of opposite polarity to be trapped simultaneously.